Answer:
Harry's opportunity cost for going to his parents is not going to his friend's birthday party.
Step-by-step explanation:
Harry has got a weekend off. He can use that weekend to paint his apartment or go fishing. He can also visit his parents for dinner. Or he can go to his friend's birthday party.
With so many options Harry is confused, about what he should do. The most important commitments for him are going over to his parent's house and attending his friend's birthday party.
If he chooses to visit his parents, the opportunity cost is not going to the party.
The opportunity cost of a decision is the cost of sacrificing the second-best alternative. The second-best alternative in this decision is attending the birthday party. So it will be considered the opportunity cost.